Machines for making laboratory analyses



Dec. 1, 1970 L. M. VAILLS 3,544,272

MACHINES FOR MAKING LABORATORY ANALYSES Filed Jan. 2. 1968 4 Sheets-Sheet 1 Dec. 1-, 1970 M. VAILLS 3,544,272 MACHINES FOR MAKING LABORATORY ANALYSES Filed Jan. 2, 1968 4 Sheets-Sheet 2 1, 1970 L. M. VAILLS 3,544,272

MACHINES FOR MAKING LABORATORY ANALYSES Filed Jan. 2, 1968 4 Sheets-Sheet 3 91 J J00 o 0 Dec. 1, 1970 M. VAILLS MACHINES FOR MAKING LABORATORY ANALYSES 4 Sheets-Sheet 4 Filed Jan. 2. 1968 United States Patent Int. (:1. oiu 1/00 U.S. Cl. 23-253 7 Claims ABSTRACT OF THE DISCLOSURE A machine for performing laboratory analyses involving fluids to be mixed in test tubes, characterised in that it comprises syringes for delivering said fluids, said syrrnges having a pneumatically-operated piston, the test tubes being disposed on supports responsive to stepbystep driving means, the length of each feed step corresponding to the relative spacing between adjacent test tubes, so that the test tubes are caused to move and stop under said syringes, the pneumatic syringe actuating means being timed with said step-by-step drive. At least two syringes have a common pivot, permitting one syringe to change fluid in a test tube while the other co-acts with its test tube and a rinsing vessel.

The present invention relates to machines for making laboratory analyses and has specific reference to an improved machine of this type, for performing laboratory analyses involving the cyclical mixing of fluids in test tubes, this machine being designed for performing this cycle automatically while increasing the performance rate in comparison with manual processes and eliminating any risk of errors.

Basically, the machine according to this invention is characterised in that it comprises fluid-delivering syringes having a pneumatically controlled piston, the test tubes being disposed on supports driven step-by-step, each feed step corresponding to the relative spacing between the test tubes so that the test tubes are caused to move and stop under the aforesaid syringes, the pneumatic means for controlling said syringes being operated in synchronism with said step-by-step driving means.

This invention is also concerned more particularly with an arrangement of the machine which is intended for carrying out successive dilutions by a series of test tubes, and characterised on this specific point in that said dilutions are effected by using at least one syringe mounted for vertical movement and a pneumatically operated piston in order to pick up and transfer the fluid from one test tube to another. Preferably and advantageously the aforesaid dilutions are carried out by using two syringes mounted on a pivoting support whereby these syringes are brought alternatively, upon each change of test tube series, the one in the dilution position and the other in a position in which it co-acts with a rinsing vessel by being immersed into said vessel while the dilution syringe is immersed into the test tubes.

Other features and advantages of this invention will appear as the following description proceeds.

A specific form of embodiment of a machine according to this invention is described hereinafter by way of example with reference to the accompanying drawing, inwhich:

FIG. 1 is a perspective view showing the upper portion of the machine;

FIG. 2 is a fragmentary front elevational view of the machine, showing the means for driving the test tube supports;

3,544,272 Patented Dec. 1, 1970 2a shows details of the resilient test tube retainmg rings;

FIG. 3 is a fragmentary side elevational view of the assembly shown in FIG. 2;

FIG. 4 is a plan view of a device for driving one of the baskets of FIG. 1 which carries the test tube supports;

FIG. 5 is an elevational view taken in the direction of the arrow V of FIG. 4;

FIG. 6 is a fragmentary view taken in the direction of the arrows VI -VI of FIG. 4;

FIG. 7 is a detail view taken in the direction of the arrow VII of FIG. 4; and

FIG. 8 is a diagrammatic view illustrating the machine driving system.

The machine illustrated in FIG. 1 comprises at its upper portion a table 1 for handling the test tubes 2; overlying this table are syringes S1 to S5 disposed above a test tube transfer path 3, the test tubes being divided in this example by groups or series of five and mounted on supporting plates 4 adapted to travel successively along said transfer path 3. These supporting plates 4 are transferred from a feed basket 5 to said transfer path 3, said basket 5 being adapted to receive a relatively great number of test tube supporting plates 4 and to bring these plates in succession to a position in which they are aligned or co-planar with the inlet of said transfer path, these plates 4 being delivered from the transfer path outlet to a similar basket 6 constituting a receiving basket.

To this end, the baskets 5 and 6, as will be explained presently, are each equipped with drive means adapted to move the relevant basket in a direction transverse to said path 3, that is, in the direction of the arrows A and R, respectively, as the plates 4 travel along said transfer path 3.

The plates are driven step by step along this path 3, as will be seen in the following description, from means so designed that each step corresponds to the relative spacing of the test tubes on the plates 4.

The transfer path 3 consists at its bottom of grooved rollers 7 adapted to be engaged by the lower edge of said plates 4, and laterally of belt rollers 8 rotatably mounted on vertical shafts, and receiving a plate-driving endless belt 9 provided to this end with studs '10 adapted to engage corresponding holes 11 disposed at spaced intervals in the plates 4. These studs 10 and holes 11 are equally spaced so that they lie at the same level or height when the corresponding supporting plate 4 is being transferred along and by the path 3.

Each plate has its upper marginal portion, which is to emerge above the path 3, formed with cutouts 12 corresponding in shape to the vertical axial section of the test tubes, the side edges of these cutouts being formed with two pairs of registering and vertically spaced notches adapted to receive test tube retaining resilient rings 14 split at 14a and notched at 1417 so as to resiliently engage the cutouts 12 and lock the test tubes in the notches 13 (FIG. 2a).

The endless belt 9 is internally notched or toothed and mounted on a loosely rotating pulley 15 and on a driving pulley 16 driven intermittently by adequate means.

To this end the mechanism driving the pulley 16 comprises a unidirectional coupling device 18 mounted on the pulley shaft 17 extending downwards under the table 1, this device 18 consisting for example of a freewheel of the wedging type adapted to drive the shaft 17 in the direction of the arrow B of FIGS. 2 and 8, the driving member of this wheel being solid with a radial arm 20 connected via a link 21 to the crankpin 22 mounted on a rotary wheel 23. This wheel 23 is driven continuously from an electric motor 24 by means of a transmission belt 25, and the shaft incorporated in the union receiving the needle thereof.

4 actuator;

26 carrying said wheel 23 has keyed-thereon a plurality of control cams C for a purpose to be explained presently.

From the onset it ,will be seen that, the rotary motion of the motor-24ris thus converted into a reciprocating motion of.arm 20 which during each half-revolution of ing syringe), while-the other syringe is'caused to dipinto a non-return device is associated with shaft 17 inthe form of-a ratchet wheel 27 engaged by a spring-urged pawl 28 lessbelt 9 and-therefore the test tube supporting plates 4 will. be drivenstep-by-step, since the length ofeach op: erative. stroke of; the endless. belt ,9 corresponds'to the relative spacing of the test tubes "in a same series. At the same time the above-mentioned cams C perform one com: plete revolution each time the endlessbelt'9, is driven by one step, and another series of control cams A is carried by a shaft 30parallel to shaft 26 and operatively con nected thereto through a train of reducing gears 31 such that the shaft 30 will complete a revolution each time five test tubes have been fed, .taking due account of the fact that the successive test tube series areseparated by two steps. In the above-described example the analysis process com-: prises both the delivery of. fluids into the test tubes and the successive dilutions thereof,. the first function being effected by the syringes S1, S2 and S5 mounted in fixed positions vertically above the test tube. stopping positions, the other function being performedbythe syringes, S3 and ,S4 of which the specific mounting will be explained presently.

Each fixedsyringe S1, S2 and S5 comprises a syringe body 32 in which a piston 33 is slidably mounted, as usual, this piston however having the additional function of the piston'of a pneumatic actuator in a. cylinder 34 formed integrally with thesyringebody, the corresponding actua tors being designated by the reference, symbols V1, V2

.andVS.. .i

Eachactuator aforesaid is of the single-acting type in thatit comprises aspring 35 normally urging, the piston 33 to its suction position, and a control chamber 36 connected through duct means to acompressed-air,distributing electromagnetic valve. Moreover, each syringe body is connected via a suction valve 38 and a feed'pipe to a fluid reservoir; thus, syringe S1 isconnectedthrough pipe .40 to-a bottle 40, like syringe S2 (through pipe 42), and

Eachsyringe body further comprises a delivery ,valve 45 The syringes S3.and .84 like the above-described syringesare associatedwith: single-acting piston-cylinder On the other hand, a pivotal motion about the rod 47 produced by another double-acting pneumatic actuator V7 of which the piston-rod 48 carries .a pin 49 engaging an elongated hole formed in a lug rigid with said support 46.

Thepurposeof this two-syringe combination S3, S4 is to permit an alternative, operation of these syringes, such that one syringe located vertically above the path 3 will be used to make the successive dilutions between the testtubes of a same series by picking up and transferring fluid from one test tube to another (as a consequenceof the vertical movement and of the operation of the correspond- .of this machine, in the exampleillustrated and described actuators designated by the reference symbols V3 and V4 a washing vessel 51 for undergoing an internal rinsing operation, whereby the permutation of syringes S3 and S4 takes place each time afresh series of test tubes is substituted for-the preceding one, asa consequence of the pivotal movementof, the common support 46 of these syring'es. i s p The pneumatic actuator V1 is connected via a pipe line 52-to a single-acting electromagnetic .valve E supplied with compressed air from a main line 53connected to the source (not shown) and to the other electromagnetic valves to. be mentionedpresently. t

Actuator V2 is connected through a pipeline 54 to a single-acting electromagnetic vvalve E Actuator. V3 is connected-viaa pipe 1ine55 to a singleacting electromagnetic valve E Actuator V4 is connected via a pipeline 56 to a singleacting electromagneticvalve E Actuator-V5 is'connected via "a pipe line 57 to a singleacting electromagnetic valve'E Actuator V6 is connected via a pair of pipe lines 58 and 59 to a double-acting electromagnetic valve E Actuator V7 is connected via a pair of pipe lines 60 and 61 to a double-acting electromagnetic valve E The function of c'ams'C and A consists in controlling electric. contacts for energizing'the'afore said electro magnetic valves and therefore 'thesyringes associated therewith as a function of the feed movement of the test tube supporting plate 4 along the path- 3 and also of the mixing and dilution program common to all the series of test tubes'to be procc'ssed 'in the machine.

Fromthe onset it. will benoted that thentimingbetween the cam controlling the cycle of operationof the syringes and the test tube supporting plates 4 is of positive nature since the internally notched belt 9 angularly connected to the cams will drive the plates 4 only as a consequence of -the engagement of said. studs 10 into the holes formed in these plates, by reason of one per 'test tube series; in other words, there is a constant, predetermined relationship between the cam positions and .the test tube positions on path 3.

trolling'the energization of the electromagnetic-valves otherwise stated, as the cams A perform one complete revolution "per test tube series, every six steps, their only function during the cycle is' to validate the pulses controlling said electromagnetic valves which are 'delivered by the other cams C making a complete revolution at each step.

The analysis process governing the cycle of operation herein; correspondstoWrig'hts veterinarian serodiag'nosis applied to cows, 0.2 cubic centimeter of serum to be analysed being placed, manually, for each cow inthe first test-tube of each series.

In this case the various syringes have the following specific functions: i

Syringe S introducing 0.5 cc; of physiological serum intojthe last four test'tubes of each' series.

. into the first test tube;

Either of the alternately used syringes S and S pickin'g-up' 0.5 cc. of serum fromthe first test tube-and transfer it into the second. test tube; v

-Picking upfrom'said second test tube 0.5 cc. of the dilution just created therein, and subsequently transfer 7 same info the third test tube; and soforth from the third. test tube into the fourthHone, and from the fourth one ino the fifh one. In other. words, there will remain 0.5 cc. in each one of the five test tubes after their passage under the dilution syringe, the serum to be analysed being gradually and increasingly diluted, the

dilution syringe completing its cycle with 0.5 cc. of the last dilution which are eliminated in the washing vessel 51, after the syringes S and S have been exchanged for making the dilutions in the next test tube series (on the contrary the syringe being rinsed must be emptied into the washing vessel before exchanging the syringes, thus introducing a differentiation in their control as will be explained presently).

Syringe S introducing 0.5 cc. of antigen into each test tubes.

The arrangement of cams C and A and of the electric contacts inserted in the circuits of the aforesaid electromagnetic valves is illustrated in FIG. 8 and will be described presently in conjunction with the operation of the machine in order to simplify the disclosure.

It will be seen, beforehand, that various electric contacts signalling the presence of the test tube supporting plates 4 engaged in the transfer path 3 are provided, these contacts being adapted to co-act with the lower edge of said plates 4, and comprising a presence contact 60 disposed beneath and between the svringes S and S another presence contact 61 located beneath the dilution syringe S or S and a third presence contact 62 underlying the syringe S The operation of this machine, from the time a test tube supporting plate 4 is engaged in the path 3 of which the belt 9 is started by energizing the motor 24, takes place as follows:

Assuming that the timing of cams C and of the supporting plate 4 engaged in the path 3 is set as explained hereinabove by engaging the studs 10 into holes 11, the supporting plate 4 will close a presence contact 60 when the first series of test tubes is positioned under the syringes S and S From the syringe arrangement illustrated in FIG. 1 it will be seen that the first actuator to be operated is actuator V and therefore its electromagnetic valve E so that this syringe S will deliver 0.5 cc. of physiological serum into the second test tube. This desired result is obtained by virtue of cams C and A and it will be seen that cam C is adapted to close an electric contact 65 having its input connected to one terminal of a suitable source of current 66 and its output connected to the input of three electric contacts 67, 68 and 69. The other terminal of said source of current is connected to the electromagnetic valves and to a relay 72.

Contact 67 responsive to cam A has its output connected to electromagnetic valve E via contact 60.

Thus, in the specific case of syringe 8,, the presence contact 60 being closed, cam A will enable the control of electromagnetic valve E during the four steps out of six of the cycle which corresponds to the passage of the last four test tubes of each series under the syringe S and cam C making one revolution per step will deliver each time the positive pulse for controlling the actual operation of this electromagnetic valve E through one fraction of the half-revolution of this cam which corresponds to the short pause observed by the test tubes at each step.

In the case of syringe S actuated thereafter, as the presence contact 60 is closed, it is cam A; that will enable the control of electromagnetic valve E during the desired step fraction which is the fraction corresponding to the pause of the first test tube of each series under the corresponding syringe S2, and it is still cam C that will deliver the positive pulse for controlling the actual operation of electromagnetic valve E In the case of syringe S disposed near the outlet of transfer path 3, it is necessary firstly that the test tube supporting plate 4 actuates the presence contact 62 to permit the operation of electromagnetic valve 13;, via contacts 65 and 69. The control of electromagnetic valve E is enabled by cam A during the five steps of the cycle corresponding to the passage of the five test tubes of each series under the syringe, and it is cam C that delivers at each step the positive pulse for controlling this electromagnetic valve (considering the positions of the syringes and test tubes shown in FIG. 2 it will be noted that cam A must be shaped to enable the control of said electromagnetic valve one step before the validation pulse delivered by cam A Syringes S and S operated by actuators V V V and V comprise specific circuits for controlling the electromagnetic valve E of the actuator for the up and downward movements of syringes V the electromagnetic valves E and E of pumping cylinders V V and the electromagnetic val've E controlling the syringe exchange actuator.

The syringes S and 8,; must perform five times the descending and ascending strokes at each cycle, since the dilution syringe must operate in all the test tubes. Therefore the control circuit of electromagnetic valve E is responsive to a cam A co-acting with a contact for valida tion during five steps of the cycle, this contact 70 being connected on the one hand to the source of current and on the other hand to the input terminal of a contact 71 controlling the descending and ascending movements.

This contact 71 has two output terminals connected respectively to the two solenoids of the double-acting electromagnetic valve E the alternate energization of one or the other of these two output terminals depending on the engagement of the control arm of this contact with a cam C performing a complete revolution during each step and delivering through this contact a down-stroke control pulse slightly inferior to the half-revolution corresponding to the stoppage of the test tubes, the remaining fraction of the revolution corresponding to an up-stroke control pulse.

Of course, this circuit is operative, i.e. a down-stroke can take place, only if the two corresponding blades of the presence contact 61 are in their closed position.

The electromagnetic valves E and E controlling the pumping cylinders V and V must be controlled differently accordingly as the corresponding syringe is operated for diluting or washing. In fact, the dilution syringe is raised, at the end of the cycle of a series, with 0.5 cc. of the last effective dilution which, for the sake of convenience, will be rejected into the washing vessel 51 in which continuous water flushing is maintained, but only after the syringe permutation, While the Washing syringe proper contains at the end of the cycle 0.5 cc. of rinsing water which must be discharged into the vessel before exchanging the syringes for the next series.

As a result the washing syringe will be actuated as a pump six times per cycle, by effecting the syringe permutation during the feed corresponding to the first step of the cycle of each test tube series, Whereas the dilution syringe will be actuated as a pump only five times per cycle. This difference in the control of electromagnetic valves E and E is obtained firstly with the assistance of a relay 72 comprising two control reversing blades inserted in the energizing circuit of these electromagnetic valves, the energization of the relay being controlled by a contact 73 responsive to the syringe positions, and actuated for example by the control arm 49 when the syringe S is in its dilution position (see FIG. 8).

A cam C driven through one revolution during each step is provided for delivering pumping control pulses in conjunction with an electric contact 75, and it will be seen that in this arrangement two pulses per cam revolution are delivered in order to double the pumping action (and thus improve the dilution and rinsing effects), these pulses being produced during the half-revolution of the cam which corresponds to the pause in the test tube step-bystep movement. These pulses issuing from contact 75 are fed directly via blade L of contact 61 and blade L of relay 72 to the electromagnetic valve E or E according as the syringe being washed is 8;, or S so that the wash pumping takes place six times per cycle as mentioned hereinabove.

' Since. the ,dilution syringe .must be actuated only five times per cycle as already explained, the pumping pulses produced by cam C and transmitted from contact .75 are also applied to this end to a contact 76 mechanically connected to said contact 70 and actuated by cam A enabling these pulses to be effective during only five steps of the cycle, "as already explained. These validated pulses are then fed to electromagnetic valve E3 or E according as the syringe performing the" dilution is S or S via blade D of presence contact 61 and blade D of relay 72.

. Finally, the electromagnetic valve E controlling the syringe exchange actuator V is actuated in this case simplyby means of an electric contact 77 responsive to a cam A revol-ving by reason of one revolution per cycle, 3'

this cam A 'being shaped and timed to cause'said con,- tact '77 to deliver a control pulse tothe electromagnetic valve E, at the beginning of the feed movement of the first step of each cycle, whereby the syringe exchange is completed atthe end of this first step. This pulse isdelivered alternatively. to one andto'the other solenoidsof said double-acting.eleetromagnetic valve E1, as a functioii of the pos'itiotr'of a're'versing blade F or 'relayf 72, and also via the blade P of presence contact 61.

The test tube supporting plates 4 are conveniently in troduced into the transfer path 3 and received at the outlet end thereof by means of feed baskets 5 and receiving baskets 6 comprising each on their bottom vertical guide rollers 80 for guiding and properly spacing the test 'tube supporting plates 4. These baskets are also provided with lateral rods 81 pivotally mounted on arms fulcrumed on shafts 82 and adapted to retain the supporting plates 4 on the relevant basket when the latter is being handled by means of the handles 83. In FIG. 1 it will be seen that when a basket is brought to its operative position'on the machine its pivotally mounted rod 81 is raised automatically on the transfer path side by engaging a ramp 84 provided to this end on the machine.

The baskets 5 and 6 are further driven in the direction Acsimilar device is provided. fordriving the receiving basket, except that the stop switchcontrolling the basket feed is located at a position 106 on the table of the ma chine, in alignment with the transfer path 3, so that it is actuated; by-thesupportingplate:41at the endof the travelthereof inthe basket (FIG. 1). r ..;Of.:.c,ourse,- the above-described form of embodiment lends, itself to, many; modifications and variations without departing from the spirit and scope of the invention as of the arrows A and R by means of respective devices illustrated in FIGS. 5, 6 and 7; each device comprises two driven endless belts 85 having their top run flush with the table surface provided to this end with a corresponding aperture, these belts being provided with driving studs 86 adapted to engage holes 87 formed in the bottom of each basket, these studs being aligned with these holes when the basket is engaged between guide members 88 secured on the machine, the weight of the-basket also bearing against slide members 89 secured to the table of the machine.

"These endless belts 85 are also of theinternally notched set; forth-,in-the appendedclaims.

What i s .cla imed is: a 1.;1A machine.v for performing, laboratory analyses involving successive dilution -to.be carried out by series-oftest tubes, said machine comprising a plurality of syringes for making said dilutions, each one of said plurality of syringes .having a pneumatically, operated. piston, supports forfthe ..test tubes, step-by step driving means operatively connected to drive said supports with thestroke of .eachfeed step, corresponding to the relative spacing 20 between adjacent test tubes so that the test tubes are caused to sequentially move-andstop under said syringes, a rinsing vessel, a common pivoting support for at least twosyring'es' mounted for vertical movement, vertical control means and pivoting control means for said common support, syringe piston control means, all said control' means being-timed in response to said step-by-step drive so that one of said syringes can pick up fluid and transfer same from one test tube to another, whereas the other of said two syringes co-acts with said rinsing vessel in which it is immersed while the other syringe is immersed in the test tubes, said common pivoting support being actuated upon' each substitution of one series of test tubes by another so that said syringes are alternatively brought one in the dilution position and the other in the rinsing position. I I

2. A machine a'ccording to claim' 1 wherein the test tube supports consist of plates disposed in a vertical plane with their lower edge engaged in a transfer path formed under the syringes, said transfer path consisting on one side of an endless belt driven in a step-by-step manner, said belt being provided with driving studs adapted to engage corresponding holes formed in each plate.

-. 3. A machine according to claim 2, wherein said stepby-step .driving means comprises a toothed driving wheel co-acting-with said endless belt formed with internal ing angular motion ;of.which-ea,chcycle corresponds to type and therefore positively driven by meansof toothed drive wheels 90 keyed on a shaft 91 carrying another toothed wheel 92 connected via an endless, internally notched transmission belt 93 to a toothed wheel 94 keyed on the output shaft. 95 of an electromagnetic clutch designated generally by the reference numeral 96. The inpnt shaft 97 'of this' clutch is constantly driven from an electric motor 98 when the machine is in operation.

In the case of the feed basket 5 the feed thereof in the direction of the arrow A may also be responsive to an end switch 99-provided at the inlet end of the transfer path 3, under the belt thereof, this switch controlling the energizationof the aforesaid electromagnetic clutch 96 for feeding the basket 5, provided that no supporting 7 plate 4 abuts thereagainst. This end switch may also be used for releasing only the basket feed, in combination with a cutout switch causing the 'basket to'stop in successive predetermined positions, such as a 'switch '100responsive to an arm.101'co1-'acting with a toothed cam 102 keyed to the drive shaft 91. This arm 101 is fulcrumed at 103 and carries a roller or follower 104 constantly urged against theteeth of cam 102 by a spring 105, so that this arm will control the final positioning of the basket each time the latter is fed, in addition to the operation of said switch 100.

' its pauses at each step of the driving means.

.4. A- machine according to claim 3, wherein said unidirectional coupling device is actuated by a connectingrod and crank mechanism comprising a rotary shaftdriving cam means rofsaid syringe piston control means, said cam means controlling electric contacts in energizing circuits of electromagnetic valves controlling in turn the I pneumatic actuation of said syringes, further contacts responsive to the presence of test tubes under the corresponding syringes making saidcircnitsoperative. 5. A machine according to claim 2, further comprising means for feeding test tube supporting. plates to said transfer path by means ofa basket guided in a transverse directionwith respect to said path andcarrying said supporting platesin -the form.of rows parallel to said path, said basket being responsive .to-intermittent drive means adapted to engage said plates into the inlet end of said path, these plates being receivedatthe outlet end of the path by a similar basketv also. driven intermittently in timed relationship. with the plate reception.

6. A machineaccording to claim 5, wherein said basket drive meanscomprises an endless-belt operatively connected to a driving motor and formed with driving studs 9 10 adapted to engage corresponding holes formed in the bot- 3,193,359 7/1965 Baruch et all 23-253 X tom of the basket. 3,269,800 8/1966 Lukrec 23--253 X 7. A machine according to claim 5, wherein said test 3,302,452 2/1967 Leslie 73-423 tube supporting plates are formed with test tube receiving 3,327,535 6/1967 Sequevia 23259 X cutouts in which the test tubes are retained by means of 3,350,946 11/1967 Isreeli 73--423 split rings resliently engaging notches formed in the side 5 edges of said cutouts and being resiliently locked therein JOSEPH SCOVRONEK, Primary Examiner by mutual engagement of notches.

US. Cl. X.R. References Cited UNITED STATES PATENTS 3,188,181 6/1965 Peterson et al. 23-253 X 

